Purge system for nitric oxide administration apparatus

ABSTRACT

A nitric oxide delivery system is disclosed that delivers a pulsed volume of NO containing therapeutic gas to a patient upon each inhalation of the patient. The NO delivery system includes certain functions to provide protection against the inadvertent inclusion of NO 2  in the therapeutic gas administered to the patient. One of the functions is to provide a purge upon start up of the delivery system apparatus that clears the regulator and conduits of any NO 2  that may have formed during the prior idle period of the system. A detector determines the start-up and may automatically carry out the purge cycle or may cause a prompt that is visual or audible to remind the user to carry out the purge cycle manually. As a further function, when the NO apparatus is terminated with respect to a patient, the system can, again, sense the termination or cessation of the therapy and automatically shut off the supply of NO containing gas at the source or provide an audible or visual prompt to remind the user to shut off the supply of the NO containing gas manually.

BACKGROUND

This invention relates to the administration of a therapeutic gas suchas nitric oxide (NO) to patients for therapeutic effect. In particular,it relates to a system wherein a controlled, predetermined dose of NO isprovided to the patient with each inhalation by the patient and to theuse of various functions utilized by that system to control and/oreliminate nitrogen dioxide (NO₂) from the system for safety reasons.

The function of the administration of NO has been fairly widelypublished and typical articles appeared in The Lancet, Vol. 340, October1992 at pages 818-820 entitled "Inhaled Nitric Oxide in PersistentPulmonary Hypertension of the Newborn" and "Low-dose Inhalational NitricOxide in Persistent Pulmonary Hypertension of the Newborn" and inAnesthesiology, Vol. 78, pgs. 413-416 (1993), entitled "Inhaled NO-thepast, the present and the future".

The actual administration of NO is generally carried out by itsintroduction into the patient as a gas and commercially availablesupplies are provided in cylinders under pressure and may be atpressures of about 2000 psi and consist of a predetermined mixture of NOin a carrier gas such as nitrogen. A pressure regulator is thereforeused to reduce the pressure of the supply cylinder to working levels forintroduction to a patient.

The concentration administered to a patient will vary according to thepatient and the need for the therapy but will generally includeconcentrations at or lower than 150 ppm. There is, of course, a need forthat concentration to be precisely metered to the patient since anexcess of NO can be harmful to the patient.

One current known method and apparatus for the administration of NO topatients is described in U.S. Pat. No. 5,558,083 where a system isprovided that can be added to any ventilator and which will meter in thedesired concentration of NO into the gas supplied from that ventilator.

Various other delivery devices have also been used that respond to thepatient attempting to inhale to deliver a pulsed dose of NO to thepatient and such pulsing devices have also been shown to havetherapeutic effect on the patient, for example, as described inHigenbottam PCT patent application WO 95/10315 and the publication ofChannick et al "Pulsed delivery of inhaled nitric oxide to patients withprimary pulmonary hypertension", Chest/109/June 1996. In such pulsatiledosing devices, a pulse of NO is administered to the patient as thepatient inhales spontaneously.

The inhalation pulsing type devices are typically shown and described inDurkan, U.S. Pat. No. 4,462,398. Another such apparatus is described inpending U.S. Patent application entitled "Constant Volume NO PulseDelivery Device", filed on May 16, 1997, U.S. patent application Ser.No. 08//57,924, which was abandoned in favor of U.S. patent applicationSer. No. 09/084,710, filed May 26, 1998, and owned by the same assignee.

One difficulty with such devices that provide a supplemental therapeuticgas to the patient concerns the formation of NO₂ from NO. NO₂ is a toxiccompound and its presence is, therefore, undesirable in any appreciableconcentration in the gas administered to the patient. Such toxic effectsare present at concentrations of about 5 ppm and therefore even minutequantities of NO₂ cannot be tolerated.

In the pulse dose devices that administer NO as a supplementaltherapeutic gas to the patient, there is likely to be no monitor tosense the presence of NO₂ and therefore it is important to takepreventative measures in the system itself to assure that the formationof NO₂ does not occur, or when it does occur, to remove the NO₂ from thesystem before the NO containing therapy gas is delivered to the patient.

The formation of NO₂ results from the reaction of NO with O₂ andtherefore there is ample opportunity in the administration of NO to apatient for NO₂ to be formed. One possibility is when the administrationdevice is connected to the NO therapy gas source, air can be trapped inthe cylinder valve and regulator fittings when the connection is madeand because the NO in the cylinder is typically only a few hundred partsper million even small volumes of air can provide enough oxygen to causesignificant proportions of the NO to react and form NO₂. Anotherpossibility is that air can be trapped in passages of the regulator andregulator pressure gauge and which are not in the main flow passages.The main passages are cleared of air during use by the flow of NOtherapy gas from the cylinder, however, when the device is turned offfor any length of time the O₂ in the air can diffuse out of thesepassages and can react with NO in the regulator and, if the cylindervalve is left open, the O₂ can diffuse into the cylinder and react withthe NO in the cylinder. The reaction of NO and O₂ to form NO₂ is a timerelated reaction, that is, the more time that the NO is in associationwith the O₂, the more NO₂ is formed, therefore it is important toprovide prevention measures wherever there is any time period where theNO and O₂ can be in contact with each other and provide means forremoving the NO₂ from the system.

Two of the rather critical periods where sufficient time can elapse andwhere NO and O₂ may intermix and where the formation of NO₂ maytherefore occur are during start-up where NO may have been left in thesystem in contact with O₂ from the prior use of the delivery system andalso after a new cylinder has been attached to the delivery device andintroduced new quantities of O₂ (in air) into the delivery device.Another critical period is the termination of the administration of NOto a patient and the delivery system shut off. At that latter time,unless the cylinder valve controlling the supply of NO containingtherapy gas is turned to the off position to isolate the NO supply fromthe NO delivery system, there is the possibility that any O₂ remainingin the conduits of the regulator during the shut down period may migrateback into the cylinder of NO containing therapeutic gas and contaminatethat cylinder of gas.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided a nitricoxide delivery system where a volume of NO is administered to thepatient and where certain safety steps are carried out to eliminate NO₂from the system to prevent the inadvertent administration of a toxicconcentration of NO₂ to the patient.

Therefore, as an aspect of the present invention, at the start up of thesystem, as indicated, there may be NO₂ that formed in the variousconduits during the time period when the delivery system was idle. Atthis point, therefore, the system may, upon the initiation of start-up,provide a visual or audible prompt to the user to carry out the purgemanually or, in the alternative, there may be an automatic purge at theinitiation of that start-up. In either case, the purge rids the systemof any NO₂ that may have formed during the time period the system wasnot in use.

As a further aspect of the present invention, the delivery systemdetects when the delivery of NO to the patient has been discontinued bythe user and the system then either senses the discontinuance of the NOadministration and provides a visual and/or audible prompt to the userso that the user can manually shut off the cylinder valve or,alternatively, automatically shuts off the cylinder valve to prevent O₂from migrating back into the cylinder thereby isolating the NO supplyfrom the various conduits and regulator of the NO delivery system.Completion of this step can be confirmed by the system by checking thatthe flow or pressure in the system goes to zero when a purge isperformed after the cylinder valve is turned off. If the valve has notbeen turned off the pressure or flow during a purge will remain atprevious levels and the system can continue the prompt to the user thatthe cylinder valve needs to be shut off.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a NO delivery system constructed inaccordance with the present invention where the user is prompted toperform the purge task;

FIG. 2 is a logic diagram for a purge scheme using the NO deliverysystem shown in FIG. 1; and

FIG. 3 is a schematic view of an alternative scheme where a purge valveis automatically actuated.

DETAILED DESCRIPTION OF THE INVENTION

Turning now to FIG. 1, there is shown a schematic view of a pulseddosing nitric oxide (NO) delivery system constructed in accordance withthe present invention. A gas cylinder 10 is provided containing thetherapeutic amount of nitric oxide. Preferable that NO gas is mixed witha balance or carrier gas such as nitrogen and the concentration may bein the order of 100 ppm. The NO in nitrogen gas is availablecommercially in cylinders at pressures of approximately 2000 psig.

Atop the gas cylinder 10 is a cylinder valve 12 and which controls thesupply of NO containing therapy gas to the overall NO delivery system.As will be explained, the cylinder valve 12 may be of the manuallyoperated type or may be controlled by a remote signal, such as by anelectrical signal operating a solenoid valve. A pressure regulator 14 islocated just downstream of the cylinder valve 12 and reduces thecylinder pressure down to a working pressure for use with the presentsystem and that pressure may be in the order of about 50 psig. Thepressure regulator 14 is connected to the cylinder 10 by a connector 13.A pressure gauge 16 is generally provided on the pressure regulator 12in order to keep track of the pressure within the gas cylinder 10.

A conduit 18 carries the NO containing therapy gas from the pressureregulator 14 through to a patient 20 where the NO containing therapy gasis administered to the patient by means such as a patient utilizationdevice 22, an example of which is a nasal cannula (not shown). It issufficient to note that the patient utilization device 22 has an openingthat communicates the NO containing therapy gas to the patient forinhalation thereof.

A control valve 30 controls the flow of NO containing therapy gas fromthe gas cylinder 10 to the patient 20 and is a solenoid controlled valveoperated by a signal from a controller 28 which may be a centralprocessing unit (CPU), logic circuit or analog circuit. Again, forsafety, the control valve 30 is preferably normally closed and is movedto its open position when a signal energizes the valve by the controller28. The control valve 30 is operated by the controller 28 in accordancewith timed or other means of sending pulses of NO containing therapy gasto the patient and the particular algorithm of control is not a part ofthe present invention.

A user input device 32 allows the user to turn the NO delivery system tothe on or the off condition. The user input device 32, at the same time,signals the appropriate condition to the controller 28. Also as a partof the system, there may be an audio alarm 34 and/or a visual display 36to alert the user to certain conditions of the NO delivery system.

A user purge input device 38 allows the user to initiate the purgecycle. The user purge input device 38, at the same time, signals theappropriate condition to the controller 28.

Sensor 40 is provided to act as a monitor of certain parameters in theNO delivery system and the sensor 40, as will become apparent, may be aflow sensor, a pressure sensor or the like and which may be connected tothe conduit 18 to sense that parameter at a location 42 between the gascylinder 10 and the pressure regulator 14, at a location 44 between thepressure regulator 14 and the control valve 30, or at a location 46between the control valve 30 and the patient utilization device 22. Asshown, the preferred location is at the location 46 and that sensorcommunication is shown as a solid line, the other locations 42 and 44are indicated as dashed lines.

Turning now to FIG. 2, there is shown a flow chart, taken along withFIG. 1, and which describes the overall operation of the NO deliverysystem. As noted, upon start-up of the system, the gas cylinder 10containing the NO therapy gas in a predetermined concentration is openedand the NO containing therapy gas enters the pressure regulator 14 andthe conduit 18. The user initiates the NO delivery system by the userinput device 32 being set to the on position, and which "on" signal iscommunicated to the controller 28.

At this point, since the NO delivery system is being initiated, there isa likelihood that some NO₂ may have formed in the conduit 18 or otherparts of the delivery system since there may have been a considerablepassage of time from the last use of the NO delivery system to allow thereacting of any remaining NO and O₂ to have occurred or a new therapygas cylinder 10 could have been connected to the delivery systemallowing air to enter the system at the connector 13. According, thesystem must be initially purged to assure that no NO₂ is present in anyof the various components.

Upon the turning "on" of the device at 60, the controller 28 activates apurge prompt at 62 to inform the user to purge the system by audio alarm34 and/or the visual display 36.

Activation of the purge at 64 by the user purge input device 38 opensthe control valve 30 for a predetermined time at 66. During that timeperiod the controller 28 determines if sufficient pressure, or flow, orthe like, was present at 68 from the signal from sensor 40. As noted,the sensor 40 may be detecting various parameters of the gas in conduit18, preferably flow or pressure.

If not, at 70 the controller 28 alerts the user that a purge was notsuccessful by audible alarm 34 and/or the visual display 36.

If the sensor 40 detected sufficient pressure, or flow, or the like, atfunction 68 the controller 28 informs the user that a purge wasperformed successfully at 72 by the audible alarm 34 and/or the visualdisplay 36.

Taking, now, the "shut down" cycle, upon the turning "off" of the deviceat 80, the controller 28 activates a purge prompt at 82 to inform theuser to purge the NO delivery system by the audio alarm 34 and/or thevisual display 36.

Activation of the purge at 84 by the user purge input device 38 opensthe control valve 30 for a predetermined time at 86. During that timeperiod the controller 28 determines if the pressure, or flow, or thelike, from the signal from sensor 40, has decayed at 88 indicating thatthe cylinder valve 12 has been closed. The controller 28 then informsthe user that a purge was performed successfully at 90 by the audiblealarm 34 and/or the visual display 36.

If the sensor 40 detects that the pressure, or flow, or the like, hasnot decayed and therefore indicating that the cylinder valve 12 has notbeen closed, then the controller 28 alerts the user that a purge was notsuccessful at 92, by the audible alarm 34 and/or the visual display 36.

Turning now to FIG. 3, again taken in connection with FIG. 2, there isshown a schematic view of an alternate to the manual purge of FIG. 1.Teed off from the conduit 18 at location 102 is a purge line 110 and apurge valve 100. As can be seen, the purge valve 100 is normally in thenon-energized position blocking the flow of gas therethrough and isactivated by controller 28 to open the purge valve 100 to clear certainportions of the conduit 18 as well as pressure regulator 14 of gas. Thelocation of the purge valve 100 could also be at locations 104 and 106.As shown, the preferred location is at the location 102 and that isshown as a solid line, the other locations 104 and 106 are indicated asdashed lines.

Again the logic as shown in FIG. 2 can apply except that the turning onof the purge prompt at 62 and the manual activation of the purge at 64are made automatic by appropriate signals from the controller 28.

Similarly, during shut down, the logic steps at 82 and 84 are automatedby the controller 28 by providing the appropriate signals.

In either event, upon the completion of the turn "on" purge cycle, thecontroller 28 will assume the control of the control valve 30 to carryout its normal function of opening and closing the control valve 30 toprovide NO containing therapy gas to the patient 20.

Accordingly, by a mandatory purge carried out automatically or by promptto the user, at the initiation of the use of the NO delivery system anda mandatory or user prompted bleed purge at the cessation of the NOdelivery system along with a verification that the NO supply has beenisolated from the delivery system, the NO₂ is effectively controlled andthe possibility of NO₂ being inadvertently introduced to the patientduring the NO therapy is greatly minimized.

Numerous further variations and combinations of the features discussedabove can be utilized without departing from the spirit of the inventionas defined by the claims below. Accordingly, the foregoing descriptionof the preferred embodiment should be taken by way of illustrationrather than by way of limitation of the invention as claimed.

We claim:
 1. A method for purging a nitric oxide delivery system of anoxygen containing gas to avoid the production of nitrogen dioxide in thesystem, said method comprising the steps of:placing the system in anactive state in which the system is capable of delivering nitric oxidecontaining gas to a patient; sensing the commencement of the activestate to initiate a purging of a conduit through which the nitric oxidecontaining gas is delivered from a source to a patient, the purgingbeing carried out by passing nitric oxide containing gas along theconduit for a predetermined period of time to remove oxygen containinggas from the delivery system; sensing a physical parameter of purginggas passage in the conduit to verify occurrence of the purge; anddelivering nitric oxide containing gas to a patient when the purge hasbeen completed.
 2. A method of purging a nitric oxide delivery system asdefined in claim 1 wherein said step of purging includes the step ofopening a location on the conduit and passing the nitric oxidecontaining gas into and through the conduit to vent through the opening.3. A method of purging a nitric oxide delivery system as defined inclaim 1 wherein said step of sensing a parameter comprises sensing thepressure of gas in the conduit.
 4. A method of purging a nitric oxidedelivery system as defined in claim 1 wherein said step of sensing aparameter comprises sensing the flow of gas in the conduit.
 5. A methodfor purging a nitric oxide delivery system of an oxygen containing gasto avoid the production of nitrogen dioxide in the system, said methodcomprising the steps of:placing the system in an inactive state in whichdelivery of nitric oxide containing gas to a patient is not carried out;sensing the inactive state of the system and thereafter sealing a sourceof nitric oxide containing gas to avoid production of nitrogen dioxidein the source from oxygen containing gases in the system; and purging aconduit by which the nitric oxide containing gas is delivered from thesource to a patient, the purging being carried out by passing nitricoxide containing gas along the conduit for a predetermined period oftime to remove oxygen containing gas from the delivery system.
 6. Amethod of purging a nitric oxide delivery system as defined in claim 5further including the step of sensing a physical parameter of thepurging gas passage in the conduit to verify occurrence of the purgingand sealing of the source of nitric oxide containing gas.
 7. A methodfor purging a nitric oxide delivery system of an oxygen containing gasto avoid the production of nitrogen dioxide in the system, said methodcomprising the steps of:placing the system in an active state in whichthe system is capable of delivering nitric oxide containing gas to apatient; sensing the commencement of the active state to initiate apurging of a conduit through which the nitric oxide containing gas isdelivered from a source to a patient, the purging being carried out bypassing nitric oxide containing gas along the conduit for apredetermined period of time to remove oxygen containing gas from thedelivery system; and delivering nitric oxide containing gas to a patientwhen the purge has been completed.
 8. A method of purging a nitric oxidedelivery system as defined in claim 7 wherein said step of purgingincludes the step of opening a location on the conduit and passing thenitric oxide containing gas into and through the conduit to vent throughthe opening.
 9. A method for purging a nitric oxide delivery system ofoxygen containing gas to avoid the production of nitrogen dioxide in thesystem, said method comprising the steps of:placing the system in anactive state in which the system is capable of delivering nitric oxidecontaining gas to a user; sensing the commencement of the active stateto provide a prompt to a user of the system calling for the initiatingof a purging of the system; sensing a physical parameter of gas passingin the conduit as a result of a user initiated purge to verifyoccurrence of the purge; and delivering nitric oxide containing gas to auser when the purge has been completed.
 10. A method of purging a nitricoxide delivery system as defined in claim 9 further defined as providinga further prompt to a user indicating that a purge has taken place. 11.A method of purging a nitric oxide delivery system as defined in claim 9wherein said step of sensing a parameter comprises sensing the pressureof the nitric oxide containing gas in the conduit.
 12. A method ofpurging a nitric oxide delivery system as defined in claim 9 whereinsaid step of sensing a parameter comprises sensing the flow of thenitric oxide containing gas in the conduit.
 13. A method for purging anitric oxide delivery system of an oxygen containing gas to avoid theproduction of nitrogen dioxide in the system, said method comprising thesteps of:placing the system in an inactive state in which delivery ofnitric oxide containing gas to a user is not carried out; sensing theinactive state of the system to provide a prompt to a user of the systemcalling for a user initiated sealing of a source of nitric oxidecontaining gas and a user initiated purging of a conduit by which thenitric oxide containing gas is delivered from the source to a user, thepurging being carried out by passing nitric oxide containing gas alongthe conduit for a predetermined period of time to remove oxygencontaining gas from the delivery system to avoid production of nitrogendioxide in the source from oxygen containing gases in the system; andsensing a physical parameter of the purging gas passage in the conduitto verify occurrence of the purging and sealing of the source of nitricoxide containing gas.
 14. A method for purging a nitric oxide deliverysystem of oxygen containing gases to avoid the production of nitrogendioxide in the system, said method comprising the steps of:placing thesystem in an active state in which the system is capable of deliveringnitric oxide containing gas to a user; sensing the commencement of theactive state to provide a prompt to a user calling for the initiation ofa purging of the system; and delivering nitric oxide containing gas to auser when the purge has been completed.
 15. A method for purging anitric oxide delivery system of an oxygen containing gas to avoid theproduction of nitrogen dioxide in the system, said method comprising thesteps of:placing the system in an inactive state in which delivery ofnitric oxide containing gas to a user is not carried out; and sensingthe inactive state of the system to provide a prompt to a user callingfor a user initiated sealing of a source of nitric oxide containing gasand a user initiated purging of a conduit by which the nitric oxidecontaining gas is delivered from the source to a patient, the purgingbeing carried out by passing nitric oxide containing gas along theconduit for a predetermined period of time to remove oxygen containinggas from the delivery system to avoid production of nitrogen dioxide inthe source from oxygen containing gases in the system; and deliveringnitric oxide containing gas to a user when the purge has been completed.